1. Field of the Invention
This invention relates to a liquid jet recording head which ejects liquid to produce flying liquid droplets to record.
2. Description of the Prior Art
Ink jet recording methods (liquid jet recording methods) have recently attracted attention since noise upon recording is very little and high speed recording is possible and, further, the recording can be made on plain paper without any special treatment such as fixation.
Among methods for example, a liquid jet recording method disclosed in Japanese patent Laid-open No. 51837/1979 and German patent Laid-open (DOLS)No. 2843064 is different from other liquid jet recording methods in that heat energy is applied to liquid to produce a driving force for ejecting liquid droplets. That is, the above-mentioned recording method comprises applying heat energy to a liquid to cause an abrupt increase in the volume of the liquid, ejecting the liquid from the orifice at the front of the recording head to form flying liquid droplets and attaching the droplets to a record receiving member to effect recording.
In particular, the liquid jet recording method disclosed in DOLS No. 2843064 can be not only effectively used for so-called "drop-on-demand" recording methods, but it also enables realization of a high density multi-orifice recording head of a full-line type, and therefore, images of high resolution and high quality can be produced at a high speed.
The recording head portion of an apparatus used for the above-mentioned recording method comprises a liquid ejecting portion constituted of an orifice for ejecting liquid and a liquid flow path containing, as a part of the construction, a heat actuating portion communicated with the orifice and applying heat energy to the liquid for ejecting liquid droplets, and an electrothermal transducer for generating heat energy.
The electrothermal transducer is provided with a pair of electordes and a resistive heater layer connected to the electrodes and having a region generating heat (heat generating portion) between the electrodes.
A typical embodiment of the structure of such liquid jet recording head is shown in FIG. 1 (a) and FIG. 1 (b).
FIG. 1 (a) is a partial front view of the liquid jet recording head viewed from the orifice side, and FIG. 1 (b) is a partial cross sectional view taken along the dot and dash line XY of FIG. 1 (a).
Recording head 100 is constituted of orifice 104 and liquid ejecting portion 105 formed by bonding the surface of substrate 102 provided with electrothermal transducer 101 to a grooved plate 103 having a predetermined number of grooves having a predetermined width and depth at a predetermined line density such that the grooved plate covers the substrate. In FIG. 1, the recording head has a plurality of orifices 104, but the present invention is not limited to such an embodiment and a recording head having a single orifice is also within the scope of the present invention.
Liquid ejecting portion 105 has orifice 104 ejecting liquid at the end and heat actuating portion 106 where heat energy generated by electrothermal transducer 101 is applied to liquid to form a bubble and an abrupt state change due to expansion and shrinkage of the volume occurs.
Heat actuating portion 106 is located above heat generating portion 107 of electrothermal transducer 101, and a heat actuating surface 108 where heat generating portion 107 contacts the liquid is the bottom suface of the heat actuating portion 106.
Heat generating portion 107 is constituted of lower layer 109 provided on substrate 102, common electrode 113 provided on lower layer 109, insulating layer 114 provided on common electrode 113, resistive heater layer 110 provided on insulating layer 114, and upper layer 111 provided on resistive heater layer 110. Resistive heater layer 110 is provided with electrodes 112 and 113 for flowing electric current to the layer 110 to generate heat. Insulating layer 114 is sandwiched in between electrodes 112 and 113. Electrode 112 is a selection electrode for selecting the heat generating portion of each liquid ejecting portion to generate heat, and electrode 113 is an electrode common to heat generating portions of liquid ejecting portions and is provided along the liquid flow path of each liquid ejecting portion.
Upper layer 111 serves to protect chemically and physically resistive heater layer 110 from the liquid at the heat generating portion 107 by isolating resistive heater layer 110 from the liquid in the liquid flow path at liquid ejecting portion 105. Upper layer 111 also serves to prevent electric leakage between adjacent electrodes. In particular, it is important to prevent electric leakage between selection electrodes and electrolytic corrosion of electrodes caused by electric current flowing in an electrode resulting from contact of an electrode under the liquid flow path with the liquid which happens by some cause. Therefore, such an upper layer 111 having a protective function is provided on at least an electrode which is disposed under a liquid flow path.
A liquid flow path provided in each liquid ejecting portion is communicated with a common liquid chamber (not shown) storing the liquid to be fed to the liquid flow path at the upstream, and in general, an electrode connected to the electrothermal transducer in the liquid ejecting portion is provided for reasons of design such that the electrode passes under the common liquid chamber at the upstream portion from the heat actuating portion. Therefore, the upper layer is also provided at the portion so as to prevent the electrode from contacting the liquid.
However, since an electrode passes under a heat generating portion in the prior art recording head, the material for the electrode is limited to that of high heat resistance, and since the insulating layer is formed to double as a heat accumulating layer, upon fabrication there are formed so many through-holes that the yield of the apparatus is low. In addition, since the prior art heat generating portion is composed of several layers as is clear from the above-mentioned examples and each layer is composed of a material different from material of other layers, the coefficient of thermal expansion is different from one another and when heat is frequently applied, an internal strain is accumulated resulting in the formation of cracks and poor durability.